In general, an electric vehicle is configured to take in electric power from an overhead wire with a current collector and drive an electric motor with a power converting device such as an inverter using the taken-in electric power to travel.
In the electric vehicle, when the brake is applied to a car, a so-called regenerative brake that regeneratively operates an electric motor to obtain a brake force is used. Regenerative power generated at this point is supplied to loads such as air conditioners of other power-running cars and cars present near the own car via an overhead wire, a third rail, and the like and consumed by the loads.
However, in the early morning, at night, and a quiet railroad section, other cars are sometimes absent near the own car (regenerative loads are insufficient). The regenerative power generated by the regenerative brake is sometimes not sufficiently consumed. When the regenerative power of the own car is larger than electric power consumed by the other cars, an overhead wire voltage rises. It is likely that various devices connected to the overhead wire are tripped or broken by an overvoltage.
Therefore, when the overhead wire voltage rises, an inverter device performs regeneration squeezing control for squeezing the regenerative brake and suppressing the generation of the regenerative power. In this case, because a regenerative braking force is reduced by the regeneration squeezing control, the reduced and insufficient brake force is supplemented by a friction brake.
On the other hand, the use of the friction brake leads to exhausting a part of kinetic energy of the electric vehicle, which is originally capable of performing power regeneration, to the atmosphere as heat. Therefore, there is a problem in terms of energy saving.
Therefore, a system has been developed in which a power storage device such as a secondary cell or an electric double layer capacitor is mounted on an electric vehicle and regenerative power is stored in the power storage device according to necessity to obtain a stable regenerative brake even when regenerative loads are insufficient (see, for example, Patent Literature 1). Note that the electric power stored in the power storage device can be used when the electric vehicle accelerates next time. Therefore, power saving is attained.
The electric vehicle mounted with the power storage device can travel on a non-electrified route without a facility of an overhead wire. In this case, the electric vehicle drives an electric motor and accelerates using only electric power from the power storage device. Regenerative power generated by the electric motor during braking is entirely stored in the power storage device.